Manufacture of pulp from fibrous substances



Feb. 5, 1963' F. NETTEL MANUFACTURE OF PULP mou FIBROUS SUBSTANCES FiledAug. 11, 1958 United States Patent Ofiice 3,076,739 Patented Feb. 5,1963 3,076,739 MANUFACTURE OF PULP FROM FIBROUS SUBSTANCES FrederickNettel, 173 Chapel Road, Manhasset, N.Y.

Filed Aug. 11, 1958, Ser. No. 754,317 7 Claims. (Cl. 162--17) Thisinvention deals with improvements in the conversion of fibroussubstances, in particular wood, straw, bagasse for examples, into pulp.Known processes work either on the batch system or the continuoussystem. In the batch system the raw material in form of chips orcuttings is fed into large so-called digester containers where it issubjected to the action of suitable chemicals (liquor) in the presenceof steam at pressures mostly above atmospheric for long periods, beingdischarged periodically. Continuous digesters use tubes through whichthe raw material is moved by mechanical means, mostly screws. Thedisadvantages of the batch digesters are principally in the slowness ofthe action, the losses incurred in steam and time-when filling them,heating them and discharging them. The continuous digesters are moreflexible in operation, give more uniform pulp, but they requirecomplicated, expensive and often unreliable means for feeding the rawmaterial into the pressure space of the digesters consisting of one ormore tubes through which the processed material is moved mostly byscrews arranged inside the digester tubes. The devices used for bringingthe raw material into the pressure space are either power-driven screws,or power-driven multi-cell rotary feeders. Such devices require muchpower and have to be designed to operate at widely different speeds toregulate the digester output, which makes them unduly expensive in firstcosts and in maintenance, because of wear.

It is known to be advantageous, and even necessary in some cases, toimpregnate the raw chips before cooking. This is done in knowncontinuous digesters either by presoaking the chips or cuttings withliquor prior to pressing the material into the pressure zone, or byusing the first tube as impregnating tube into which liquor is fedtogether with steam. Pre-soaking at atmospheric pressure does not givesatisfactory results because the liquor generally has to be at elevatedtemperatures to be chemically really effective.

Using the first tube as impregnating tube is expensive in the sense thatthe chips or cuttings do not have to be moved for good impregnation.Besides, the recovery of surplus liquor from the impregnating tubewithout clogging in the piping is known to cause difficulties.Re-circulating the liquid after re-fortificating it during theimpregnation is known to be advantageous, economical and because itshortens the necessary cooking time.

It is the main object of this invention to provide in substantiallycontinuous digesters simple and cheap means for impregnating the rawmaterial, while at the same time eliminating the complicated and costlydevices for bringing the material from a space (hopper) underatmospheric pressure into the pressure zone or zones of the digesters.In general it may be said that I attain this principal object of myinvention, as well the other objects thereof which will hereinafterappear, by providing a plurality of closed chambers, preferably two innumber, each with valved connections with a source of raw material, forexample an open hopper, and with the pressure zone of the digester. Theraw material is fed into said chambers in sequence, beginning with thefirst chamber with its valve to the digester closed. After filling iscompleted, the valve to the hopper is also closed and steam is admittedand liquor circulated through said chamber so that impregnation of theraw material is achieved. While this takes place, the valves of thesecond chamber to the digester and to the hopper were kept closed,however, when the impregnation in the first chamber starts, the valve ofthe second chamber to the hopper is opened and filling starts, and whencompleted, impregnation in the second chamber proceeds in the samemanner as described for the first chamber. In the meantime impregnationin the first chamber has been completed to a desired degree, whereuponsurplus liquor is drained from it and then its valved connection to thefirst digester tube of the continuous digester is opened and thecontents discharged into the latter. When this discharge is completed,the impregnation in the second chamber has also been completed andsurplus liquor is drained from it. Then the valved connection of thefirst chamber with the digester is closed and the valved connection ofthe second chamber with the digester tube is opened and feeding of thelatter from the second chamber begins. Now the pressure in the firstchamber is suitably relieved, its valved connection with the hopperopened and filling from the hopper is repeated. The cycle is now closedand is repeated in the same manner over and over again, resulting in asubstantially continuous feeding of the digester, because the switchingover of feeding from one chamber to the other which by themselvesoperate on the batch principles can be completed in a few seconds. It isanother object of my invention to provide the valves for the material,liquor and steam with controls which operate these elements in thesequence indicated above, completing the operating cycle in apredetermined and adjustable time, called for the purposes of thisspecification the cycle time.

It is a further object of my invention to vary the cycle tilme inrelationship with the required output of the digester p ant.

The volume (chip capacity) of the sluice-impregnation chambers isdetermined by the nature of the raw material to be processed, the typeof liquor used, and the product quality desired. At present animpregnation period, i.e. a residence time of the chips in each chamber,of not less than ten percent of the whole pulping cycle time ispreferred.

It is immaterial for the purposes of my invention whether impregnationtakes place at the same or a pressure difierent from that which prevailsin the digester tubes. Obviously, the pressure in the chambers will beequalized with that in the digester tubes when the valved connections tothe latter are opened. It is also immaterial for the purposes of myinvention what fibrous raw material is used and what chemicalcomposition the liquor has.

In the drawing affixed to this specification and forming part thereof,an embodiment of this invention is illustrated diagrammatically by wayof non-limiting example as follows:

It shows a digester with two closed sluicing and impregnation chambersand two cooking tubes. 1 is the open hopper with outlet conduits 2 and 3and interposed gate valves 4 and 5. 6 and 7 are the two closed sluicingand impregnation chambers with outlet conduits 8 and 9 with interposedgate valves Y10 and 11. Conduits 8 and 9 discharge into conduit 12 whichis connected to the one end of the first cooking tube 13 with internalscrew 14- which is driven by a motor 15. At the other end of tube 13 aconduit 16 connects with the second cooking tube 17 which is essentiallyof the same design as the tube 13, also driven by a motor 18. Theconduit 19 is connected with the discharger 26 for the cooked pulp whichleaves the plant through pipe 21. At the lower end of the hopper 1 twovalved steam pipes 21 and 22 are provided to facilitate the discharge ofthe raw chips from the hopper. The valved pipes 23 and 24 serve to admitsteam under pressure into the chambers 6 and 7, and the valved pipe 25permits to connect the chambers 6 and 7 with the atmosphere. Alsoconnected with both chambars are liquor impregnating and circulatingmeans consisting of liquor tanks 26 and 27 from which liquor can bepumped by pumps 28 and 29 driven by motors 28 and 29' through the pipes30 and 31 with valves 30 and 31' into the upper parts of the chambers 6and 7. The liquor returns to said tanks via the pipes 32 and 33. Fresh(white) liquor is fed into said tanks through the valved pipes 34 and35. All the valves shown, with the exception of those in pipes 21, 22,34 and 35, are power operated from a common control cylinder 36, drivenby a motor 37. This cylinder receives an operating medium, for exampleoil under pressure, at 38. The control connections to each of saidvalves are indicated diagrammatically only by broken lines. Steam mayalso be admitted to the first cooking tube through the valved pipe 3?.The drawing shows the plant at a moment when the chamber 7 isdischarging into the digester While the chamher 6 is being filled.Obviously the valves in pipes 21, 22., 34 and 35 may also be poweroperated from the cylinder 36, if desired. Starting, and operating ofthe plant, assuming both chambers 6 and 7 empty and the gate valves 4,5, 10 and 11 closed, proceeds after starting the motor 37 of the controlas follows; gate valve 4 is opened and chamber 6 filled, assisted bysteam jet from pipe 21. Gate valve 4 closed, steam admitted through pipe23, pump 23 started by motor 28' and valve 30' opened, so thatimpregnation of the chips in the chamber 6 can proceed, and by keepingthe pump in operation recirculation of the liquor impregnation isspeeded and improved. In the meantime, after starting impregnation inchamber 6, gate valve is opened and filling of chamber 7 starts in thesame way, and when completed, gate valve 5 is closed, steam admittedthrough pipe 24, pump 29 started by motor 29' and valve 31 opened, sothat impregnation in the chamber 7 proceeds in the same manner asdescribed above for chamber 6. In the meantime impregnation in thechamber 6 has been completed, whereupon the pump 28 is stopped, valve 30closed, so that surplus liquor is drained from chamber 6 via pipe 32into the liquor tank. Thereafter gate valve is opened and theimpregnated chips are discharged into the cooking tube 13, assisted bysteam jet from pipe 23. After the chamber 6 is empty, the impregnationwhich has been proceeding in the chamber 7', is also completed so thatsurplus liquor is drained from it via pipe 33 by stopping pump 29 andclosing valve 31. Now gate valve 10 is closed and the steam pressure inthe chamber 6 is relieved either to the atmosphere via pipe 25 with3-way valve or by opening gate valve 4 slowly, thereby loosening andmoistening the chips at the entrance of chamber 3, making it ready forthe next filling. After gate valve 10 has been closed, the gate valve 11is opened and discharge of the chamber 7 into the digester beginsimmediately, practically without interruption of the feeding of thedigester. The feeding and impregnation cycle is now completed and isrepeated by the filling of the chamber 6.

For regulating the output in continuous digesters it is known toregulate the speed of the motors and 18 and thereby the speed at whichthe pulp is moved through the cooking tubes by the screws 14. Obviously,it is necessary to correlate the feeding from the chambers 6 and 7 withthe required output and this is achieved by my invention by regulatingthe speed of the motor 37 driving the control cylinder 36.

The use of sluices to introduce materials into a pressure zone is knownper se. This invention teaches as new the combination of special sluicechambers With continuous digesters, and effecting an important part ofthe pulping process, i.e. the impregnation of the raw material, underthe simultaneous application of liquor and steam under pressure Withintwo or more alternatingly operating sluice chambers, with predeterminedtime intervals provided for the impregnation, eliminating also the heavy4 power demand for operating known devices such as screw feeders ormulti-cell feeders.

Manifestly, variations may be resorted to, equivalents of partsintroduced, and parts may be used without others Within the broad scopeof my invention and its features.

Having now described my invention, I claim:

1. Method of producing pulp from fibrous materials in a continuousdigester by subjecting them to the chemical action of a liquor andsteam, comprising the steps of charging the comminuted raw material intothe inlet of a first chamber, thereafter closing the inlet and outlet ofsaid first chamber so as to isolate it, admitting steam and liquor underpressure into said isolated chamber, circulating the liquor through saidfirst chamber in a substantially closed first circuit so as toimpregnate the raw material therein, then draining surplus liquor fromsaid first isolated chamber while maintaining the inlet closed, thenopening the outlet of said first isolated chamber, then discharge thecontents of said first chamber into the pressure zone of the digester,repeating said steps with a second chamber and the same digester, thefilling of the second chamber with said raw material being timed tooccur during the impregnation of said raw material in the first isolatedchamber, and thereafter repeating the cycle alternatingly with the firstand second chambers and with the same relative timing, with the liquorcirculating through said second chamber means in a second substantiallyclosed circuit.

2. Method of producing pulp from fibrous raw materials in a highpressure continuous digester by subjecting them to the chemical actionof a liquor and steam, comprising the steps of closing the outlet of afirst cham ber, charging the comminuted raw material into the inlet ofsaid first chamber, thereafter closing the inlet of said first chamberso as to isolate it, admitting steam and liquor under low pressure intosaid isolated first chamber, circulating the liquor through said firstchamber in a first substantially closed circuit so as to impregnate theraw material therein, then draining surplus liquor from said firstisolated chamber while maintaining the inlet closed, opening the outletof said first isolated chamber to the higher pressure zone of thedigester so as to admit this higher pressure to the first chamber, thendischarge the contents of said first chamber into the digester under thehigher pressure, repeating said steps with the second chamber and thesame digester, the filling of the second chamber with said raw materialbeing timed to occur during the impregnation of said raw material in thefirst isolated chamber, and thereafter repeating the cycle alternatinglywith the first and second chambers and with the same relative timingwith the liquor circulating through said isolated second chamber in asecond substantially closed circuit.

3. In a continuous digester for comminuted fibrous material, thecombination of a digester in which the fibrous material is subjected tothe action of steam and liquor under pressure for chemical treatment ofsaid material, open container means for the raw material, two chamberseach having an inlet and outlet, conduit means including first valvemeans for connecting selectively each of the said inlets of said twochambers with said open container means, conduit means including secondvalve means for selectively connecting each of the outlets of said twochambers with the digester, a source of liquor, conduit means includingthird valve means forming a first substantially closed circulatory pathfor said liquor through the said first chamber and a secondsubstantially closed circulatory path for said liquor through saidsecond chamber, pumping means for circulating the liquor separatelythrough each of said circulatory paths, conduit means including fourthvalve means for introducing steam under pressure into, and forwithdrawing steam from said chambers, control means for operating thevalve means and pumping means in said conduit means in predeterminedsequence and in repetitive cyclic order, said control means includingmeans for closing the second valve means, means for opening the firstvalve means between said open container means and said first chamber forfilling it with raw material, means for then closing the first valvemeans serving said first chamber, means for then opening the third andfourth valve means to the first chamber for liquor and steam, means forthen energizing the pumping means serving the first chamber forcirculating liquor through said chamber so as to effect impregnation ofthe raw material during a predetermined period, means for then openingsaid first valve means between said open container means and the secondchamber for filling said second chamber with raw material whileimpregnation is proceeding in said first chamber, means for then closingsaid first valve means to said second chamber after filling of saidsecond chamber with raw material, means for then opening the third andfourth valve means serving the second chamber for introducing liquor andsteam into said second chamber, means for then energizing the liquorpumping means serving the second chamber so as to effect impregnation ofthe raw material therein during a predetermined period, means for thenclosing said third and fourth valve means serving said second chamber,means for then deenergizing said pumping means for the second chamber,means for then opening the second valve means from the first chambersoas to discharge the contents of said first chamber into the digester,means for then closing said second valve means from the first chamber,means for then opening the second valve means serving the second chamberso as to discharge the contents of the second chamber into the digester,mean-s for then closing said second valve means for the second chamber,means for opening the first valve means to the first chamber while theimpregnation of the raw material is proceeding in said second chamber.

4. In a continuous digester as set forth in claim 3, valved conduitmeans for introducing into said closed chambers steam of difierentpressure than prevails in the digester tubes and to maintain saiddifferent pressure at least during part of the time While impregnationtakes place in said chambers.

5. In a continuous digester as set forth in claim 3, valved steamconduits connectable to both said chambers, to relieve rcssure in thesaid chambers to a space of lower pressure.

6. In a continuous digester as set forth in claim 3, a liquor tankinterposed in the circuit of liquor circulation and valved conduit meansfor introducing fresh liquor into the said circuit.

7. In a continuous digester as set forth in claim 3, means forregulating the digester output by valve control means disposed tocomplete the cycling operation of the valves in time intervalsdecreasing with increasing output of the digester.

References Cited in the file of this patent UNITED STATES PATENTS

1. METHOD OF PRODUCINT PULP FROM FIBROUS MATERIALS IN A CONTINUOUSDIGESTER BY SUBJECTING THEM TO THE CHEMICAL ACTION OF A LIQUOR ANDSTEAM, COMPRISING THE STEPS OF CHARGING THE COMMINUTED RAQ MATERIAL INTOTHE INLET OF A FIRST CHAMBER, THEREAFTER CLOSING THE INLET AND OUTLET OFSAID FIRST CHAMBER SO AS TO ISOLATE IT, ADMITTING STEAM AND LIQUOR UNDERPRESSURE INTO SAID ISOLATED CHAMBER, CIRCULATING THE LIQUOR THROUGH SAIDFIRST CHAMBER IN A SUBSTANTIALLY CLOSED FIRST CIRCUIT SO AS TOIMPREGNATE THE RAW MATERIAL THEREIN, THEN DRAINING SURPLUS LIQUOR FROMWITH A SECOND CHAMBER AND THE SAMME DIGESTER THE FILLING CLOSED, THENOPENING THE OUTLET OF SAID FIRST ISOLATED CHAMBER, THEN DISCHARGE THECONTENTS OF SAID FIRST CHAMBER INTO THE PRESSURE ZONE OF THE DIGESTER,REPEATING SAID STEPS WITH A SECOND CHAMBER AND THE SAME DIGESTER, THEFILLING OF THE SECOND CHAMBER WITH SAID RAW MATERIAL BEING TIMED TOOCCUR DURING THE IMPREGNATION OF SAID RAW MATERIAL IN THE FIRST ISOLATEDCHAMBER, AND THEREAFTER REPEATING THE CYCLE ALTERNATINGLY WITH THE FIRSTAND SECOND CHAMBERS AND WITH THE SAME RELATIVE TIMING, WITH THE LIQUORCIRCULATING THROUGH SAID SECOND CHAMBER MEANS IN A SECOND SUBSTANTIALLYCLOSED CIRCUIT.